Fixture for holding a rod guide assembly of a fuel control unit of an aircraft engine during welding

ABSTRACT

A method of repairing a rod guide assembly of a fuel control unit of an aircraft engine is provided. The method comprises disconnecting a used spring seat from the rod of the rod guide assembly and welding a replacement spring seat to the rod using an electron beam controlled using a circular beam deflection pattern.

FIELD

This relates generally to engine maintenance, and more particularly tomaintenance of fuel control units of aircraft engines.

BACKGROUND

Maintenance of aircraft engines is often mandated to occur at prescribedintervals to ensure performance and reliability. Such maintenance mayresult in the destruction and replacement of some components in order toperform the required maintenance. Replacement of such components can becostly.

SUMMARY

According to an aspect, there is provided a method of repairing a rodguide assembly of a fuel control unit of an aircraft engine where a usedspring seat has been disconnected from the rod of the rod guideassembly. The method comprises:

welding a replacement spring seat to the rod by:

with the rod disposed on a first side of a wall of the replacementspring seat, directing an electron beam toward the wall of thereplacement spring seat from a second side of the wall opposite thefirst side; and

controlling the electron beam using a circular beam deflection pattern.

According to another aspect, there is provided another method ofrepairing a rod guide assembly of a fuel control unit of an aircraftengine. The method comprises:

disconnecting a used spring seat from the rod of the rod guide assembly;and

welding a replacement spring seat to the rod using an electron beamcontrolled using a circular beam deflection pattern.

According to another aspect, there is provided a fixture for holding arod guide assembly of a fuel control unit of an aircraft engine duringwelding. The fixture comprises:

a base;

a first clamp counterpart movably coupled to the base, a position of thefirst clamp counterpart being adjustable along a clamping direction;

a second clamp counterpart coupled to the base and spaced apart from thefirst clamp counterpart along the clamping direction; and

a rod seat coupled to the base and disposed between the first clampcounterpart and the second clamp counterpart, the rod seat beingconfigured to engage with the rod of the rod guide assembly and keep alongitudinal axis of the rod in substantial alignment with the clampingdirection.

Other features will become apparent from the drawings in conjunctionwith the following description.

BRIEF DESCRIPTION OF DRAWINGS

In the figures which illustrate example embodiments,

FIG. 1A is a schematic axial cross-sectional view of a gas turbineengine;

FIG. 1B is a schematic diagram of an example compressor dischargepressure (CDP) rod guide assembly components installed in a fuel controlunit for a gas turbine engine;

FIG. 2A is a side view of an upper portion of the CDP rod guide assemblyof the fuel control unit in a state prior to welding a replacementspring seat to a rod of the CDP rod guide assembly;

FIG. 2B is a side perspective view of the CDP rod guide assembly of thefuel control unit in a state after welding the replacement spring seatto the rod of the CDP rod guide assembly;

FIG. 3 is a cross-sectional view of a welded CDP rod guide assembly;

FIG. 4A is a flowchart of a method of repairing a rod guide assembly ofa fuel control unit of the engine;

FIG. 4B is a flowchart of another method of repairing a rod guideassembly of a fuel control unit of the engine;

FIG. 5 is an illustration of a CDP rod guide assembly mounted to anexample welding fixture; and

FIG. 6 is a perspective view of another example fixture for weldingmultiple CDP rod guide assemblies.

DETAILED DESCRIPTION

Aspects of various embodiments are described through reference to thedrawings.

FIG. 1 is a schematic representation of an exemplary turboshaft engine10. It is understood that aspects of the present disclosure may beapplicable to other types of gas turbine engines. Engine 10 maycomprise, in serial flow communication, air intake 12 through whichambient air is received, multistage compressor 14 for pressurizing theair, combustor 16 in which the compressed air is mixed with fuel andignited for generating an annular stream of hot combustion gases,turbine section 17 for extracting energy from the combustion gases, andexhaust duct 18 via which the combustion gases exit engine 10. Engine 10may also include fuel control unit 19 that may be used to control fuelflow to combustor 16.

FIG. 1B is a simplified diagram of components of an example rod guideassembly installed in fuel control unit 19. The fuel control unit 19 mayregulate the flow of fuel being delivered to combustor 16 of engine 10via suitable fuel nozzles. As depicted in FIG. 16, the fuel control unit19 may include fuel metering valve 4 and bellows assembly 6 connectedvia compressor discharge pressure (CDP) rod guide assembly 5. In someembodiments, fuel control unit 19 may also include a fuel metering valvearm, a spring, a manual contact point and an electronic enginecontroller (EEC) mode contact point.

In some embodiments, the amount of fuel delivered to the fuel nozzlesmay be a function of various parameters. One such parameter is thecompressor discharge pressure of gas turbine engine 10. Changes incompressor discharge pressure may affect the position of fuel meteringvalve 4 and bellows assembly 6. In response to changes in compressordischarge pressure, rod 510 of CDP rod guide assembly 5 (depicted inFIGS. 2A and 2B) may be displaced along body 515, while spring seat 505of CDP rod guide assembly 5 interacts with a fuel metering valve spring(not shown).

After a certain period of time, engine 10 may require maintenance (e.g.,an overhaul). An overhaul may require taking apart and inspectingvarious components of engine 10, including fuel control unit 19. Anoverhaul may be required after a pre-defined performance threshold hasbeen reached. Such a threshold may include a pre-defined amount of timein operation, a pre-defined number of takeoff and landing cycles, apre-defined distance travelled, or the like.

In some embodiments, maintenance tasks may include disassembly,cleaning, inspection, repair or replacement of certain components andassembly(ies), and testing of fuel control unit 19. In some situation,disassembly of fuel control unit 19 may require the destruction of CDProd guide assembly 5. In other words, disassembly of fuel control unit19 may require rendering CDP rod guide assembly 5 unsuitable forcontinued use and therefore require replacement of CDP rod guideassembly 5.

FIG. 2A is a side view of an upper portion of CDP rod guide assembly 5in a state prior to welding replacement spring seat 505 to rod 510.Replacement spring seat 505 may include hole 503 extending through wall505A (see FIG. 3) at future weld region 520 (see FIG. 2B) and mayfacilitate welding using electron beam welding. In some embodiments,hole 503 may have a diameter of about 0.8 mm. Hole 503 may extendradially relative to a longitudinal axis of rod 510.

FIG. 2B is a side perspective view of an example CDP rod guide assembly5. In some embodiments, CDP rod guide assembly 5 may have an overallheight along rod 510 of about 2.5 cm. As depicted, CDP rod guideassembly 5 may include spring seat 505, rod 510, and body 515. Springseat 505 may be substantially circular in profile and may include acentral hole configured to receive rod 510. The term “substantially” asused herein may be applied to modify any quantitative representationwhich could permissibly vary without resulting in a change in the basicfunction to which it is related. Spring seat 505 may be secured to rod510 so that spring seat 505 and rod 510 may move together. In someembodiments, rod 510 may be configured to freely slide or otherwise bedisplaced along body 515 via a hole extending into body 515.

To perform an overhaul of fuel control unit 19, CDP rod guide assembly 5may be removed from fuel control unit 19. Previously known maintenancepractices for such components require users to dispose of the entire CDProd guide assembly 5 and replace it with a new CDP rod guide assembly 5each time an overhaul is performed on fuel control unit 19. As such, itis wasteful to replace a used CDP rod guide assembly 5 with a new CDProd guide assembly 5 each time an overhaul is performed. Moreover, CDProd guide assemblies 5 are costly.

There is no known method for overhauling fuel control unit 19 withoutdisposing of CDP rod guide assembly 5. During an overhaul of fuelcontrol unit 19, it may be necessary to disconnect spring seat 505 fromrod 510 without any way of re-securing spring seat 505 to rod 510 thatis suitable for continued use of CDP rod guide assembly 5. For example,spring seat 505 and rod 510 may be secured by way of a weld orotherwise, and disconnecting spring seat 505 from rod 510 may includemachining and/or grinding spring seat 505 from rod 510 for example. Inother words, disconnecting spring seat 505 from rod 510 may result indestroying spring seat 505.

In some embodiments, methods disclosed herein may allow components ofthe CDP rod guide assembly 5 of fuel control unit 19 to be salvaged andre-used after an overhaul. For example, the methods disclosed herein mayallow for a replacement spring seat 505 to be secured to the existing(i.e., used) rod 510 in a suitable manner permitting the re-use of rod510 and of body 515.

FIG. 3 is a cross-sectional image of an upper portion of CDP rod guideassembly 5 showing a replacement spring seat 505 after having beenwelded to rod 510 at weld region 520. In some embodiments, thereplacement (i.e., new) spring seat 505 can be welded to rod 510 at weldregion 520 using electron beam welding with a circular deflectionpattern, which may be suitable for welding such relatively small parts.For example, in some embodiments, a thickness T of wall 505A of springseat 505 at weld region 520 may be about 0.8 mm before welding. Invarious embodiments, the thickness T of wall 505A of spring seat 505 atweld region 520 may be between 0.5 mm and 1 mm before welding. In someembodiments, a diameter D of a portion of rod 510 to be welded to springseat 505 may be about 1.6 mm. In various embodiments, the diameter D ofthe portion of rod 510 to be welded to spring seat 505 may be between1.5 mm and 1.8 mm. In some embodiments, a penetration L of a weldbetween rod 510 and wall 505A of spring seat 505 may be about 0.75 mm.In some embodiments, penetration L of a weld between rod 510 and wall505A of spring seat 505 may be between 0.5 mm and 1.5 mm.

Rod 510 may have a cylindrical shape with a circular outercross-sectional profile. Wall 505A of spring seat 505 at the location ofweld region 520 may be at least partially annular and extend partiallyaround rod 510. Wall 505A of spring seat 505 may define a receptacleinto which an end of rod 510 is received. In some embodiments, rod 510and spring seat 505 may both be made from a martensiticprecipitation-hardening stainless steel (e.g., type 17-4 PH).

FIG. 4A is a flowchart of a method 100 of repairing rod guide assembly 5of fuel control unit 19 of engine 10. Method 100 may comprise:

disconnecting used spring seat 505 from rod 510 of rod guide assembly 5(see block 102); and

welding replacement spring seat 505 to rod 510 using an electron beamcontrolled using a circular beam deflection pattern (see block 104).

FIG. 4B is a flowchart of another method 200 of repairing rod guideassembly 5 of fuel control unit 19 of engine 10. Aspects of methods 100and 200 may be combined together. Method 200 may comprise:

disconnecting used spring seat 505 from rod 510 of CDP rod guideassembly 5 of fuel control unit 19 (see optional block 202); and

welding replacement spring seat 505 to rod 510 by:

with rod 510 disposed on a first side of wall 505A of the replacementspring seat 505, directing an electron beam toward wall 505A of thereplacement spring seat 505 from a second side of wall 505A opposite thefirst side (see block 204); and

controlling the electron beam using a circular beam deflection pattern(see block 206).

The first side of wall 505A may be a radially-inner side of wall 505Aand the second side of wall 505 may be a radially-outer side of wall505A.

Spring seat 505 may be placed in a pre-welding configuration with rod510. Such pre-welding configuration may be a positioning of spring seat505 in close proximity (e.g., in physical contact) with rod 510 so as topermit welding (e.g., via hole 503).

In some embodiments, a replacement spring seat 505 may be fabricated orobtained and welded to rod 510. It is contemplated that methodsdisclosed herein may also be suitable for welding an original springseat 505 to rod 510.

Using electron beam welding, a pattern generator can be programmed toprovide a customizable oscillation pattern. Such oscillation pattern mayallow for a beneficial effect on the depth-to-width ratio, beadappearance, and consistency of welding performance. A low frequencydeflection system can be used to produce a circular movement in a smallarea, which has the effect of “stirring” the weld pool. The deflectionpattern can be selected to achieve precise control over the fusion zoneshape and over surface heat treatment patterns and cooling rate. In someembodiments, the electron beam welding device is configured to performthe weld using pre-defined operating parameters. In some embodiments,these operating parameters include one or more of a current of about 2mA, a voltage of 120 kV, a speed of about 58 cm/minute, a frequency ofabout 2 Hz, and/or a circular deflection pattern. It has been found thatsuch operating parameters may yield a weld suitable for securing springseat 505 to rod 510. The use of electron beam welding with a circulardeflection pattern may allow for precise control over the weld in therelatively small weld region 520.

The circular deflection pattern may be suitable for welding at thelocation of circular hole 503 (shown in FIG. 2A) by having the electronbeam cause melting of the material at the edge of hole 503. For example,the electron beam may be controlled to follow the edge of hole 503 andcause melting of the material at the edge of hole 503. The diameter of acircular path followed by the electron beam may be slightly larger thanthe diameter of hole 503.

As depicted in FIG. 3 weld region 520 may be disposed on one side of rod510. In some embodiments, the electron beam welding may result in anunderfill along wall 505A of spring seat 505. In some embodiments, weldregion 520 may have a depth of about 0.4 mm. In some embodiments, anexample penetration depth of weld region 520 relative to the radiallyoutermost point of wall 505A of spring seat 505 may be about 1.5 mm. Itshould be noted that these dimensions are merely examples and may varybetween different parts, applications and welding parameters.

FIG. 5 is an illustration of a replacement spring seat 505, rod 510 andbody 515 held in the pre-welding configuration by welding fixture 600.As depicted, welding fixture 600 may include screws 650 a, 650 b whichcan apply pressure to spring seat 505 and body 515 (i.e. both ends ofCDP rod guide assembly 5), to provide clamping and/or contact betweenspring seat 505 and rod 510 during the electron beam welding process.

Fixture 600 may include base 602, a first clamp counterpart, a secondclamp counterpart and rod seat 604. One or both first and second clampcounterparts may be movably coupled to base 602. Accordingly, a positionof one or both first and second clamp counterparts may be beingadjustable along clamping direction C. The first clamp counterpart mayinclude a threaded fastener such as screw 650A, threadably engaged withfirst protrusion 606 disposed on (e.g., extending from) base 602. Thesecond clamp counterpart may include a threaded fastener such as screw650B, threadably engaged with second protrusion 608 disposed on (e.g.,extending from) base 602. Screws 650A and 650B may be coupled to base602 and spaced apart from each other along clamping direction C.

Rod seat 604 may be coupled to base 602 and disposed between screws650A, 650B. Rod seat 604 may be configured to engage with rod 510 of CDProd guide assembly 5 and keep a longitudinal axis of rod 510 insubstantial alignment with clamping direction C. Rod seat 604 mayinclude a slot formed in third protrusion 610 disposed on (i.e.,extending from) base 602.

Placing replacement spring seat 505 and rod 510 in a pre-weldingconfiguration may include securing (e.g., clamping along clampingdirection C) spring seat 505, rod 510 and body 515 in welding fixture600 via screws 650A, 650B and rod seat 604. Welding fixture 600 may thenplaced inside an electron beam welding device to perform the weld.Screws 650A, 650B may be used to axially clamp spring seat 505 to an endof rod 510 to permit welding of spring seat 505 and rod 10 together. Insome embodiments of fixture 600, rod 510 and screws 650A, 650B may besubstantially coaxial when CDP rod guide assembly 5 is mounted infixture 600.

FIG. 6 is an isometric view of another example welding fixture 6000having elements in common with welding fixture 600. Like elements areidentified using like reference numerals. Welding fixture 6000 maydefine multiple stations for receiving respective CDP rod guideassemblies 5 to be welded in a batch. Welding fixture 6000 may bemodified to define a desired number of stations. As depicted, weldingfixture 6000 may include base 602 and protrusions 606, 610 and 608extending from base 602. Protrusions 606, 610 and 608 may be shaped asbars. Protrusion 606 may be spaced apart from middle protrusion 610 todefine a gap suitable for receiving spring seat 505. Protrusion 606 mayhave a plurality of threaded holes formed therein and adapted to receiverespective screws 650A for each station. Protrusion 608 may be spacedapart from protrusion 610 to define a gap suitable to accommodate body515 of CDP rod guide assembly 5. Protrusion 608 may have a plurality ofthreaded holes formed therein and adapted to receive respective screws650B for each station. Protrusion 610 may define a plurality of rodseats 604 (e.g., slots or grooves) adapted to receive respective rods510. In some embodiments, each rod seat 604 may be aligned withcorresponding screws 650A and 650B, such that rod 510 and screws 650A,650B are substantially coaxial.

Welding fixture 6000 (or weld fixture 600 of FIG. 5) may be placed intoan electron beam welding system. An electron beam welding systemincludes a vacuum chamber with a table or platform upon which thearticle to be welded by electron beam welding is placed and secured. Insome embodiments, the electron beam welding system may be programmed toperform welds for multiple spring seats 505 and rods 510 in successionwhen multiple spring seats 505 and rods 510 are secured in weldingfixture 6000. This may be performed, for example, by configuring theelectron beam welding system to move welding fixture 6000 along apre-defined path after performing a weld on a first set of spring seat505 and rod 510. In this manner, multiple CDP rod guide assemblies 5 maybe overhauled as part of a single, pre-programmed electron beam weldingprocess. This may reduce the time required for loading the electron beamwelding apparatus compared to placing only one spring seat 505 and rod510 in the electron beam welding apparatus at a time. Moreover, theprocess of achieving a desired vacuum level within the vacuum chamber ofthe electron beam welding system is a time-consuming process, so thecapability of overhauling multiple CDP rod guide assembles 5 in a singleprocess may result in time savings.

The methods and fixtures disclosed herein are not limited for used tooverhaul CDP rod guide assemblies of fuel control units but may also beused for other applications. For example, aspects of method 100 can beadapted to secure a component to a rod where the component has a wallwith a first side for facing the rod and a second side opposite thefirst side. With the rod disposed on the first side of the wall of thecomponent, welding the component to the rod can be achieved by:

directing an electron beam toward the wall of the component from thesecond side of the wall of the component; and

controlling the electron beam using a circular beam deflection pattern.

The above description is meant to be exemplary only, and one skilled inthe relevant arts will recognize that changes may be made to theembodiments described without departing from the scope of the inventiondisclosed. The present disclosure may be embodied in other specificforms without departing from the subject matter of the claims. Thepresent disclosure is intended to cover and embrace all suitable changesin technology. Modifications which fall within the scope of the presentinvention will be apparent to those skilled in the art, in light of areview of this disclosure, and such modifications are intended to fallwithin the appended claims. Also, the scope of the claims should not belimited by the preferred embodiments set forth in the examples, butshould be given the broadest interpretation consistent with thedescription as a whole.

1.-15. (canceled)
 16. A fixture for holding a rod guide assembly of afuel control unit of an aircraft engine during welding, the fixturecomprising: a base; a first clamp counterpart movably coupled to thebase, a position of the first clamp counterpart being adjustable along aclamping direction; a second clamp counterpart coupled to the base andspaced apart from the first clamp counterpart along the clampingdirection; and a rod seat coupled to the base and disposed between thefirst clamp counterpart and the second clamp counterpart, the rod seatbeing configured to engage with the rod of the rod guide assembly andkeep a longitudinal axis of the rod in substantial alignment with theclamping direction.
 17. The fixture of claim 16, wherein the first clampcounterpart includes a first threaded fastener.
 18. The fixture of claim17, wherein the second clamp counterpart includes a second threadedfastener.
 19. The fixture of claim 18, wherein the rod seat comprises aslot formed in a protrusion disposed on the base.
 20. The fixture ofclaim 16, wherein: the first clamp, second clamp and the rod seat definea first station for holding the rod guide assembly; and the fixturecomprises a second station for holding another rod guide assembly.